8 MOSSES WITH A HAND-LENS 



central portion, causing it to assume the shape of a pie-plate. 

 This upturned margin of the columella also enables the teeth 

 to remain attached to its edge in their changed position. In 

 species of this family with more nearly erect capsules the teeth 

 are longer and often fewer in number, making the escape of the 

 spores easier. 



If you take a capsule in the condition represented in Fig. 2, 

 and place it in warm water for a few minutes, it will assume the 

 appearance shown in I, and no spore can be shaken out; although 

 a careful examination of the contents of the capsule will show 

 that the spores are not wetted, for when mounted in water they 

 are still surrounded by an envelope of air. 



The pepper-box is closed, but how? Kerner von Marilaunt 

 states that the teeth, when wet, curve inwards so strongly that 

 the columella is pressed against the mouth of the capsule, closing 

 it effectually. Five minutes' study, however, will show any one 

 that the teeth do not curve in when wet, but, instead, straighten 

 up and outwards ; the columella also expands and becomes of 

 nearly -the same diameter as the capsule. This makes the open- 

 ings lateral instead of terminal. The teeth expand enough 

 laterally so that not a single drop of water can enter or a spore 

 escape. In addition, the spores seem to be protected by the 

 nature of their outer surface, for it takes a very long soaking 

 to wet the spores so that they can be satisfactorily mounted in 

 water for microscopic study. 



Plate II, Fig. 2 shows the peristome of Hypnum in its dry 

 state. Note how the cilia fill the spaces between the segments, 

 forming a perfect sieve. Fig. I shows the same peristome wet 

 and closed so tightly that no water can get in or spores get out. 

 One can easily see from an examination of these two figures the 

 advantage of having the segments alternate with the teeth. 



This illustration is from a Hypnum with a strongly curved 

 capsule. If an illustration were chosen from a species with an 

 erect capsule the cilia would, in most cases, be more or less 

 rudimentary and the segments narrowed, as is explained in the 

 beginning of this topic. 



In Fig. 4, the dry peristome of Ceratodon purpureus is shown. 

 The loosely incurved teeth form a capital sieve. Fig. 3 shows 

 the same dry. The peristome of Dicranum, shown in Pigs. 5, 



tNat. Hist. Plants, 



